The documents
RIG: the Information Guide for Buyers and Sellers
Presented before services begin, same as on the buying side. Informational, not a commitment.
Listing Agreement (OREA Form 200)
The contract between you and the brokerage. Sets the list price, the term, the commission and how it's split, and the holdover period. Read the term and the holdover clause carefully. The holdover means commission may still be owed if you sell privately, shortly after expiry, to someone introduced during the term.
MLS Information Sheet
The data entry form behind your listing. It itemises a wide range of data points that get fed into MLS: room dimensions, taxes, lot size, inclusions and exclusions, rental items, parking and locker, condominium fees and what they cover, and dozens of smaller fields.
It is worth reading before it is submitted, because most of what a buyer's agent sees about your property comes from this sheet rather than from the marketing. An error here follows the listing everywhere it appears, and a room measured optimistically is the kind of thing that surfaces later as a credibility problem rather than a typo.
Agreement of Purchase and Sale (OREA Form 100)
The offer itself, and the same document a buyer signs. Its critical fields are the price, the deposit, the closing date, the irrevocable date, the conditions, and everything in the attached schedules. Once it is accepted by both sides and any conditions are waived, you are selling the house.
See Common Clauses for how to read one, and What Happens After the Offer Is Accepted for what follows.
SPIS: the Seller Property Information Statement
Optional in Ontario. A detailed questionnaire about the property's condition and history. Some agents recommend it, others advise against it, for reasons worth understanding.
Ontario distinguishes between two kinds of defect. A patent defect is visible on reasonable inspection, and you have no duty to point it out. A latent defect is hidden, and where it makes the property dangerous or unfit for habitation, you must disclose it. Knowingly concealing a latent defect of that kind exposes you to liability after closing.
Once you complete an SPIS, its answers become representations a buyer can rely on. That's the argument both for it (it builds trust and can head off later claims) and against it (an inaccurate answer creates a liability you wouldn't otherwise have had). This is a conversation to have with your lawyer, not a box to tick.
Disclosure obligations turn on specific facts. If you know of something about your property that worries you, raise it with a real estate lawyer before the listing goes live rather than after an offer arrives.